Variable-volume turbocharger

ABSTRACT

A variable-volume turbocharger device comprises at least two exhaust gas passages (A), (B) different in the flow characteristics, divided by a partition wall (20) provided in a turbine housing (18), and two valve members (34a), (34b) which are actuated so as to open and shut the exhaust gas passages (A), (B). The valve members (34a), (34b) each are actuated to open and shut in response to the speed and load of an engine or the likes, whereby either one of the exhaust gas passages (A), (B) or both of them are opened to provide at least three turbine flow characteristics. An exhaust gas turbine (12) can be thereby operated with remarkably good efficiency suitably to the operating state of the engine.

TECHNICAL FIELD

The present invention relates to an improvement in a turbocharger devicein which an exhaust gas turbine is driven by the exhaust gas of anengine and a compressor for pressurizing the intake air of said engineis driven by the gas turbine.

BACKGROUND ART

An engine for motor vehicles such as automobiles is operated through anextremely wide area of engine speed ranging from an idling speed to themaximum speed and within a widely varying load range, and the quantityof its exhaust gas varies by a large margin. In an exhaust gas turbinehaving a single flow characteristics, therefore, it is not possible torecover and utilize the energy of the exhaust gas discharged from anengine thoroughly. So, a variable-volume turbocharger device has beenalready proposed in which a partition wall is provided in a turbinehousing to divide the exhaust gas passage in said housing into twoexhaust gas passages different in the flow characteristics and valvemeans are provided which are switchable to open either one of saiddivided exhaust gas passages, wherein said valve means are switched overto operate in accordance with the operating conditions such as theengine speed and load, thereby to improve the operational efficiency ofthe exhaust gas turbine.

In such a conventional variable-volume turbocharger device, two turbineflow characteristics can be obtained, but it is desirable to obtainplural turbine flow characteristics suited for the operating conditionsof an engine.

The turbine housing of a turbocharger device can not be expected to behighly precise because it is manufactured by casting. Thus, it isdifficult to form said partition wall and a turbine rotor in closerelationship with high precision and a large clearance must be providedbetween the partition wall and the turbine rotor. In this case, theexhaust gas passage leading from the fore end of the partition wall tothe turbine rotor is rapidly enlarged, with a disadvantage of resultingin loss.

DISCLOSURE OF INVENTION

It is a main object of the present invention to provide avariable-volume turbocharger device improved so that more turbine flowcharacteristics suited for the operating conditions of an engine can beobtained.

In order to achieve this object, the present invention proposes avariable-volume turbocharger device comprising a turbine housing havingat least two exhaust gas passages different in the flow characteristics,divided by a partition wall, and two valve means for opening andshutting each of said exhaust gas passages selectively in response tothe operating state of an engine to make the turbine flow characteristicvariable.

According to the abovementioned composition, either one of the exhaustgas passages or both of them are opened by actuating these valve meansto open or shut suitably in response to the operating state of theengine, whereby at least three turbine flow characteristics can beobtained and the exhaust gas turbine can be operated properly and withgood efficiency. Besides, it is possible to shut both the exhaust gaspassages at the same time, thereby to exhibit the exhaust brakingfunction.

It is another object of this invention to provide a method formanufacturing a turbine housing for a turbocharger device, in which thefore end of the partition wall of the turbine housing can be formed inclose relationship to a turbine rotor, in order that a loss caused bythe rapid enlargement of its exhaust gas passage can be avoided.

To achieve this object, this invention proposes a method formanufacturing a turbine housing for a turbocharger device having atleast two exhaust gas passages different in the flow characteristics,divided by a partition wall provided in its inside, which comprisespreviously forming an end member as a separate body from said partitionwall, and then securing said end member on the inner circumferentialpart of said partition wall.

According to this method, the clearance between the fore end of said endmember and a turbine rotor can be minimized, and a loss caused by therapid enlargement of the exhaust gas passage between them can beavoided.

Furthermore, the present invention relates to a method for controlling avariable-volume turbocharger device, and proposes a method forcontrolling a variable-volume turbocharger device comprising at leasttwo exhaust gas passages different in the flow characteristics, dividedby a partition wall provided in a turbine housing, and two valve meansfor actuating each of said exhaust gas passages so that they are openedor shut, in which either one of said valve means or both of them areactuated to open in response to the operating state of an engine,thereby to provide three different turbine characteristics of large,medium and small flow rates.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a vertical sectional view of the first embodiment of thevariable-volume turbocharger device according to the invention,

FIG. 2 is an enlarged sectional view showing the turbine housing of FIG.1,

FIG. 3 is an enlarged view showing the principal part of FIG. 2,

FIG. 4 is a diagram showing the relationship between the quantity of theturbine efficiency lowered and the turbine rotor-partition wallclearance,

FIG. 5 is a diagram of the turbine flow characteristic of theturbocharger device,

FIG. 6 is a diagram of the operational characteristic of theturbocharger device,

FIG. 7 is an enlarged plan view showing the first modification of thevalve means,

FIG. 8 is a vertical sectional view taken along the line VIII--VIII ofFIG. 7,

FIG. 9 is a vertical sectional view showing the second modification ofthe valve means,

FIG. 10 is a vertical sectional view of the turbocharger device showingthe second embodiment of the invention,

FIG. 11 is an enlarged transverse sectional view showing the valve meansof FIG. 10,

FIG. 12 is an enlarged transverse sectional view showing the firstmodification of the valve means of the second embodiment,

FIG. 13 is a vertical sectional view of FIG. 12,

FIG. 14 is a partially enlarged transverse sectional view showing thesecond modification of the valve means of the second embodiment,

FIG. 15 is a vertical sectional view of FIG. 14,

FIG. 16 is a partially enlarged transverse sectional view showing thethird modification of the valve means of the second embodiment,

FIG. 17 is a general view of a turbocharger device equipped with adriving mechanism showing the third embodiment of the invention,

FIG. 18 is a partially enlarged vertical sectional view of the turbinehousing showing the fourth embodiment of the invention,

FIG. 19 is a typical view showing a core used to manufacture the turbinehousing of FIG. 18,

FIGS. 20 to 22 each are a plan view showing a different modification ofthe end member of FIG. 18,

FIG. 23 is a partially enlarged vertical sectional view of the turbinehousing showing a modification of the fourth embodiment,

FIG. 24 is a vertical sectional view of a turbocharger device showingthe fifth embodiment of the invention,

FIG. 25 is a flowchart showing the operation of the turbocharger deviceof FIG. 24,

FIG. 26 is a diagram of the operational characteristic of theturbocharger device of FIG. 24,

FIG. 27 is a vertical sectional view of the turbocharger device forillustrating a different control method,

FIG. 28 is a diagram of the operational characteristic of theturbocharger device in accordance with the first control method,

FIG. 29 and FIG. 30 each are diagram showing the operational mode inaccordance with said first control method, and

FIG. 31 is a diagram of the operational characteristic of theturbocharger device in accordance with the second control method.

BEST MODE FOR CARRYING OUT THE INVENTION

A number of embodiments according to this invention will be described indetail with reference to the accompanying drawings.

In the following descriptions and drawings, the corresponding elementshaving the same or similar function are designated by the same referencenumerals.

In the first embodiment according to this invention shown in FIG. 1 toFIG. 6, the reference numeral 10 represents generally a variable-volumeturbocharger device, 12 is an exhaust gas turbine thereof, and 14 is acompressor driven by the exhaust gas turbine 12. The exhaust gas turbine12 has a turbine housing 18 accomodating a rotor 16, and in the insideof the housing 18, there are provided exhaust gas passages, i.e. scrollsA and B divided in the direction of the rotor axis by a radial partitionwall 20, which are different in the flow characteristics. A valve casing24 mentioned below is connected to the exhaust gas inlet 22 of saidhousing 18, and the valve casing 24 is further connected with theexhaust device of an engine (not shown). This is an exhaust manifold 26in this embodiment. In the exhaust gas inlet 22, there are providedinlets 22a and 22b divided by the extended portion of the partition wall20 and each reaching down to the exhaust gas passages A, B.

The valve casing 24 is almost box-like in the external shape, and theupper wall surface thereof is provided with an upstream opening 28communicating to the exhaust manifold 26 and the lower wall surfacethereof is provided with downstream openings 30a, 30b connectingrespectively to the inelts 22a, 22b, as shown in FIG. 1. Between theupstream opening 28 and the downstream openings 30a, 30b, in thisembodiment, there are provided valve seats 32a, 32b, having seatingsurfaces on two planes which intersect each other in the V-shaped format an angle of 90° made between them, and the valve openings of thesevalve seats will be opened and shut by valve members 34a, 34b,respectively. The valve members 34a, 34b each have a protruded shafts36a, 36b on their back surface, and the protruded shafts 36a, 36b eachare supported on the free end of a rocker arm 38a, 38b, with enoughclearance existing in the radial direction, and the valve members 34a,34b each are supported on the rocker arms 38a, 38b by spherical seats.The other ends of the respective rocker arms 38a, 38b are secured on asupport shaft 40a, 40b pivotally supported on the side wall relativelyat the upstream side of the valve casing 24. The valve casing 24 hasopenings at both the right and left sides, in FIG. 1, for attachment,removal and check of the valve members 34a, 34b, and these openings arenormally closed by detachable lids 42. The reference numeral 44represents a partition wall placed in the valve casing 24 and connectingto the partition wall 20 of the turbine housing inlet 22.

In the aforementioned device, the support shafts 40a, 40b which willopen and shut the valve members 34a, 34b by way of the rocker arms 38a,38b are connected to proper actuators (not shown) such as pneumaticresponsive devices so as to be actuated to open and shut these valvemembers in accordance with the operating state of the engine (notshown), for example the engine speed and load.

In this embodiment, the flow characteristic B₂ of the exhaust gaspassage A in the turbine housing 18 is set at one larger than that B₁ ofthe passage B, as shown in FIG. 5. As for the characteristic diagramshown in FIG. 5, the corrected flow rate will be represented by theformula G√T₁ /P₁ and the expansion ratio by the formula P₂ /P₁, whereinthe designation G is the flow rate of the exhaust gas, T₁ is thetemperature of the exhaust gas at a turbine inlet, P₁ is the pressure ofthe exhaust gas at the turbine inlet, and P₂ is the pressure of theexhaust gas at a turbine outlet.

As shown in FIG. 2 and FIG. 3 showing the exhaust gas turbine 12 inenlargement, the inner peripheral surface 18a of the turbine housing 18defining the exhaust gas passage B and the inward end 16a of the turbinerotor 16 overlap each other in the direction of the axis of the turbinerotor. In FIG. 3, the inner peripheral surface 18a overlaps on theturbine rotor 16 only by a length 1 in the direction of the turbinerotor axis. After due consideration of the dimensional tolerances of ashaft 15 supported on a center housing 17 of the turbocharger device,the turbine rotor 16 and the turbine housing 18, this length l is setsuch that the inner peripheral surface 18a and the inward end 16aoverlap each other positively even when these tolerances are in theworst condition.

The clearance δ between the inner circumferential edge 20a of thepartition wall 20 and the outer circumferential edge of the turbinerotor 16 is set as follows. Representing the diameter of the turbinerotor by the letter D (see FIG. 2), the value of the abovementionedclearance δ is set such that the inequality δ/D≦0.06 is satisfied. Thereason that the clearance δ is so set will be described with referenceto FIG. 4. In FIG. 4, there is exhibited a relationship between thequantity of the turbine efficiency lowered Δηt and the turbinerotor-partition wall clearance δ/D. Assuming that the turbine efficiencyηt is 0.7 and the compressor efficiency ηc is 0.7, the overallefficiency η all=ηt×ηc becomes 0.49. When the turbine efficiency islowered 2%, the turbine efficiency ηt becomes 0.686 and the overallefficiency η all=ηt×ηc becomes 0.686×0.7=0.48. Namely, the 2% reductionin the turbine efficiency results in a lowering of about 1% in theoverall efficiency. In a case that the turbine efficiency exceeds 2% inthe maximum, the performance of the engine in the fuel consumption isnormally worsened seriously. When the turbine rotor-partition wallclearance δ/D is below 0.06, the quantity of the turbine efficiency ηtlowered becomes large suddenly with the increase in the value of theclearance δ. This means that when the turbine rotor-partition wallclearance δ/D is below 0.06 in consideration of the machining toleranceof the clearance δ, the lowering of the turbine efficiency δt varieswidely due to the variations of the clearance δ. As can be seen fromFIG. 4, accordingly, it is preferred to set the value of clearance δsuch that the inequality δ/D≦0.06 is satisfied.

In the preferred operational mode of the exhaust gas turbine 12, thestate just shown in the drawing, this is the state in which the valvemember 34a is closed but the valve member 34b is opened, stands when anengine is in a low speed, high load operation (in the region B₁ of FIG.6), and as a result, the exhaust gas from the exhaust manifold 26 passesthrough the exhaust gas passage B from the upstream opening 28, thevalve opening of the valve seat 32b, the corresponding downstreamopening 30b and the inlet 22b of the turbine housing, and acts upon theblades of the rotor 16 so that the exhaust gas turbine 12 is operatedwith efficiency, in accordance with the flow characteristic B₁ shown inFIG. 5. Under such a state, the opened valve member 34b cooperates withthe partition wall 44 to form, in the valve casing 24 at the downstreamside from the valve seat 32b, an exhaust gas passage which is almostgently bent and small in resistance, and on the other hand, the valvemember 34a which seats on the valve seat 32a included in a plane whichintersects the plane including the valve seat 32b at an angle of about90° formed therebetween, provides a portion of the passage wall at theupstream side from the valve seat 32b to form an exhaust passage whichis gently sloping and small in resistance.

When the engine is operating in a medium speed, high load state (in theregion B₂ of FIG. 6), the valve member 34a is opened and the valvemember 34b is closed, and as a result, the exhaust gas is fed to theturbine rotor 16 through the exhaust gas passage A which is larger inflow characteristic, in the mode quite similar to the abovementionedmode. Thus, the exhaust gas turbine 12 is operated in accordance withthe flow characteristic B₂ shown in FIG. 5. Also in this case, a gentlysloping passage small in flowing resistance is formed similarly to theabove case, because the valve seats and the exhaust gas passages areformed almost symmetrically at both the sides of the partition wall 44in the valve casing 24, as shown in the drawing.

When the engine is in a low load operation, without reference to itsengine speed, or in a high speed, low load operation (in the region B₃of FIG. 6), both the valve members 34a, 34b are opened together, and asa result, the exhaust gas which has flowed from the upstream opening 28into the valve casing 24 passes through the passages divided right andleft by means of the central partition wall 44, and the divided flows ofthe exhaust gas flow from the downstream openings 30a, 30b into theinlets 22a, 22b of the turbine housing respectively, and fed from boththe exhaust gas passages A, B to the turbine rotor 16. Thus, the exhaustgas turbine 12 is operated in accordance with the flow characteristic B₃shown in FIG. 5. Also in this case, the opened valve members 34a, 34bcooperate with the partition wall 44 to serve as one side wall of theexhaust gas passage.

As an example in which the present invention is applied, there may beprovided, in the exhaust gas turbine housing, a third exhaust gaspassage other than the passages A, B in the abovementioned embodiment,and the third passage in this case may be a passage having no valve ormay be adapted to be opened and shut by a third valve other than thevalve members 34a, 34b.

In the variable-volume turbocharger device according to the presentinvention, as abovementioned, at least two inlets partitioned by apartition wall are provided in the portion of a turbine housing where anexhaust gas is introduced, and these inlets are connected with theexhaust device of an engine by way of valve means, respectively. Thus,the variable-volume turbocharger device has such effects that theexhaust gas can be fed to the exhaust gas turbine in accordance with theturbine flow characteristics suited to the operated state of the engineby actuating the valve means selectively for their opening and shutting,and as a result, the turbine can be properly operated with goodefficiency.

The provision of a valve casing in which the valve seats and valvemembers are arranged in a special mode between the exhaust gas turbineof a turbocharger device and the exhaust device of an engine such as theexhaust manifold, is very advantageous, because the exhaust gas can befed to the exhaust gas turbine through a selected passage which isproper and small in flowing resistance, in response to the operatingstate of the engine, with the pressure loss of the exhaust gas reduced.As can be seen from the descriptions on the aforementioned embodiment,furthermore, it is most preferable to arrange the valve seats 32a, 32bon the planes which intersect each other at an angle of about 90° (theseplanes are not always flat planes), but it is capable to modify thisangle of intersection widely from about 60° to 120°, with obtaining thesame effects nearly. In addition, the valve casing can be manufactured,assembled and exchanged at need, as one unit, and this is convenient inpractice.

In case the turbine rotor 16 is being rotated in accordance with theflow characteristics B₃ and B₂ in FIG. 5, the leakage of the exhaust gasat the time when it flows through both the exhaust gas passages A, B orthrough the exhaust gas passage A to rotate the turbine rotor does notbecome a serious question. When the exhaust gas is caused to flow onlythrough the exhaust gas passage B, however, the leakage of the exhaustgas has a great influence upon the generation of increased pressure,because the flow characteristic B₁ of the passage B is small. Thus, inthe present invention, the turbine housing 18 and the turbine rotor 16are overlapped in the direction of the rotor axis, with an effectcapable of reducing the loss of energy due to the leakage of the exhaustgas to the utmost.

In the first embodiment mentioned above, the cross-sectional contours ofthe upstream opening 28 of the valve casing 24, the valve openings ofthe valve seats 32a, 32b and the exhaust gas passages leading from saidvalve openings to the downstream openings 30a, 30b, may be in any shapeof an oblong rounded in four corners, oval, ellipse or circle, or may bea combination of them. As a matter of course, the contour of the valvemembers 34a, 34b is preferably in a shape nearly similar to that of thevalve openings of the valve seats 32a, 32b. Furthermore, it is possibleto arrange the valve means including the valve members 34a, 34b in theinlets 22a, 22b of the turbine housing 18 by way of the rocker arms 38a,38b pivotally supported on the housing respectively, instead ofarranging them in the valve casing 24. In this case, the valve members34a, 34b will be engaged with valve seats provided at the opening partof the turbine housing inlet 22 and adapted to open toward thedownstream side in the flowing direction of the exhaust gas.

FIG. 7 and FIG. 8 show the first modification of the valve means used inthe aforementioned first embodiment, wherein it is aimed to improve thesmoothness of their opening and shutting operation and the performanceof their sealing.

As illustrated in detail by FIG. 7 and FIG. 8, the plane contour of thevalve member 34a, 34b is of a square rounded in four corners, and thevalve seat 32a, 32b which cooperates with the valve member is made in ashape nearly similar thereto, in this embodiment. In order that theclose fitting of the valve member 34a, 34b to the valve seat isprevented from being broken by the turning of the valve member 34a, 34band the rocker arm 38a, 38b around the protruded shaft 36a, 36b,therefore, the rocker arm 38a, 38b is adapted to be inserted in a groove44 provided in the valve member 34a, 34b, with a proper gap 46 existingtherebetween. The valve member 34a, 34b and the rocker arm 38a, 38bcooperate with each other by way of spherical surfaces 48 and 50 whichfit to each other, and a lock washer 52 is fixed on the protruded shaft36a, 36b by means of a nut 54. There are a proper radial clearance 56between the protruded shaft 36a, 36b and the rocker arm 38a, 38b and aclearance 58 in the direction of the axis of the protruded shaft betweenthe spherical surfaces 48 and 50.

By turning the support shaft 40a clockwise in FIG. 8 by means of theaforementioned actuator when the valve member 34a is closed, the end ofthe valve member 34a at the remote side from the support shaft 40a isfirst brought into contact with the corresponding portion of the valveseat 32a, and then the valve member 34a is guided for closure movementby the spherical surfaces 48 and 50 due to the existence of saidclearances 46, 56 and 58 so as to be fitly seated on the position shownin FIG. 8. At that time, all of the valve seat 32a, valve member 34a andprotruded shaft 36a do not undergo any unnatural force due to theexistence of said clearances, and the valve member 34a and valve seat32a can be closely fitted to each other in a proper state, ensuring anexcellent sealing property. The portions which must be relativelydisplaced from each other, this is the protruded shaft 36a and rockerarm 38a, do not adhere to each other, because there is enough clearancebetween them as mentioned above, and the support shaft 40a is also notlikely to adhere and its operation is smooth and accurate, because it isnot in direct contact with a high temperature exhaust gas. This factwill be applied similarly to the other valve member 34b.

FIG. 9 shows the second modification of the valve means according to theaforementioned first embodiment.

In the second modification shown in FIG. 9, the rocker arm 38a, 38b andthe valve member 34a, 34b are formed so as to be in contact with eachother on plane seats and the lock washer 52 is suitably secured on theprotruded shaft 36a, 36b. Also in this case, a proper clearance 56 isprovided between the protruded shaft 36a, 36b and the correspondinginsertion hole of the rocker arm 38a, 38b, and a proper clearance 58 inthe direction of the axis of the protruded shaft 36a, 36b is furtherprovided between the rocker arm and the valve member, whereby the valvemember 34a, 34b can be closely fitted to the valve seat 32a, 32bcooperating therewith, smoothly and fitly.

Although the valve members 34a, 34b of the valve means are arranged soas to be opened toward the downstream side in the flowing direction ofthe exhaust gas with respect to the valve seats 32a, 32b, in the firstembodiment according to the present invention shown in FIGS. 1 to 6, thesecond embodiment of this invention shown in FIG. 10 and FIG. 11 isdifferent from the aforementioned first embodiment, at such a viewpointthat valve members are arranged so as to be opened toward the upstreamside in the flowing direction of an exhaust gas with respect to valveseats.

In FIG. 10, the exhaust gas inlet 22 of an exhaust gas turbine 12 isdirectly connected with the outlet gathered portion 30 of an exhaustdevice of an engine. This is an exhaust manifold 26 in this embodiment.On the flat end surface of the exhaust gas inlet 22, valve seats 32a,32b are formed around inlets 22a, 22b leading to exhaust gas passages A,B, respectively. Valve members 32a, 32b which cooperate with the valveseats 32a, 32b are arranged in the outlet gathered portion 30. The valvemembers 34a, 34b each have a protruded shaft 36a, 36b on their backsurface, the protruded shafts 36a, 36b each are supported on the freeend of a rocker arm 38a, 38b, with an enough clearance existing in theradial direction, and the valve members 34a, 34b each are supported onthe free end of the rocker arm by way of spherical seats. The other endof the respective rocker arms 38a, 38b is secured on a support shaft40a, 40b which is pivotally supported through a bush on the side wall ofthe outlet gathered portion 30 of the exhaust manifold 26 connectingwith the exhaust gas inlet 22 of a turbine housing 18. In thisembodiment, there is therefore no need of providing the valve casingused in the aforementioned first embodiment, and as a result, it ispossible to compact and lighten the whole of a turbocharger device.

As illustrated in detail in FIG. 11, bushes 40c and 40d are fitted intothe side walls of the outlet gathered portion 30 of the exhaust manifold26, and the support shafts 40a, 40b each are individually inserted inthe rocker arm 38a, 38b supporting the valve member 34a, 34b by way ofthe protruded shaft 36a, 36b, and pivotally supported at both their endsin the bushes 40c, 40d.

As materials for improving the wear resistance of these members whichmust be used at high temperatures caused by exhaust gas and under anon-lubricated state, it is advantageous to use, by way of example,martensitic steel for the support shafts 40a, 40b and rocker arms 38a,38b when martensitic chromium carbide-precipitated steel is employed forthe bushes 40c, 40d, and to use martensitic chromiumcarbide-precipitated steel for the support shafts and rocker arms whenceramic such as zironia or alumina is employed for the bushes.

The support shafts 40a, 40b which serve to open and shut the valvemembers 34a, 34b are connected with actuators such as pneumaticresponsive devices by way of levers 38c, 38d, as well as theaforementioned first embodiment.

In addition, the structure of the other parts in the turbochargerdevice, especially of the turbine housing 18, is the same as in thefirst embodiment, and its operation and effect are also the same.

Furthermore, it is possible to arrange, in the valve casing, the valvemeans adapted to open toward the upstream side, similarly to theaforementioned first embodiment.

FIG. 12 and FIG. 13 show the first modification of the valve means usedin the abovementioned second embodiment.

In this first modification, the plane contour of the valve member 34a,34b is of a rectangle rounded in four corners, and the valve seats 32a,32b which cooperate with the valve member are made in a shape nearlysimilar thereto. In order that the valve member 34a, 34b and the rockerarms 38a, 38b are not turned around the protruded shaft 36a, 36b,therefore, stopper member 40e, 40f is provided. The stopper member 40e,40f is a plate having a bent portion for holding down the side wall ofthe valve member 34a, 34b, which plate is clamped on the protruded shaft36a, 36b, with the engagement of the valve member 34a, 34b therewith.

FIG. 14 and FIG. 15 show the second modification of the valve means usedin the aforementioned second embodiment.

This second modification exhibits another structure adapted to preventthe turning of the valve members 34a, 34b in the case the valve membersare not in the shape of a circle (for example, they are in a rectangle).A stopper portion 40g, 40h is integratedly protruded as a turnpreventing means on the corner of the valve member 34a, 34b at the sideof the support shaft 40a, 40b. Although the valve member 34a, 34b isgoing to turn, therefore, its turning can be prevented because thestopper portion 40g, 40h collides with the support shaft 40a, 40b.

FIG. 16 shows the third modification of the valve means used in theaforementioned second embodiment, in which the difficulty in opening ofthe valve members 34a, 34b caused by the action of the exhaust gaspressure has been taken into consideration in the case that the valvemembers are of the shape of a rectangle as mentioned above.

As seen from FIG. 16, the supporting point of the protruded shaft 36a,36b for the valve member 34a, 34b is positioned at a position staggeredto the side of the support shaft 40a, 40b with respect to thecross-sectional center of the flow passage of the valve seat 32a, 32b,and the rocker arm 38a, 38b is formed short. In order that the valvemember 34a, 34b is caused to open against the exhaust gas pressure,there is required a force having the same magnitude as the exhaust gaspressure or the differential pressure between both the sides of thevalve member, in a case that the cross-sectional center of the flowpassage and the supporting point for the valve member accord with eachother. In this modification, however, the supporting point for the valvemember 34a, 34b is offset to the side of the support shaft 40a, 40b fromthe cross-sectional center of the flow passage. In the opening operationof the valve member 34a, 34b, therefore, a working force for opening thevalve member 34a, 34b is applied to the protruded shaft 38a, 38b in sucha mode that the outer end of the valve member (on the side of thesupport shaft 40a, 40b) is first lifted up, with a portion where theinner end of the valve member (at the opposite side to the supportshaft) and the valve seat 32a, 32b are in contact with each other as afulcrum and the valve member is then opened. As a result, the exhaustgas is permitted to flow out of the gap at the outer end of the valvemember 34a, 34b and the differential pressure between both the sides ofthe valve member is reduced, whereby the force required to open thevalve member becomes small. Accordingly, it is possible to compact theactuator for opening the valve member, by offsetting the supportingpoint for the valve member, as mentioned above.

The third embodiment of the present invention shown in FIG. 17 relatesto a driving mechanism for opening and shutting the valve means used inthe aforementioned second embodiment.

The variable-volume turbocharger device according to the secondembodiment has such as structure that the valve members of the valvemeans are adapted to open toward the upstream side with respect to thevalve seats. The opening operation of the valve member 34a in an exhaustgas passage with a larger flow passage area, this is the exhaust gaspassage A, needs therefore an actuator 50a such as an air cylindercapable of giving a large working force enough to overcome a largepressure which is applied onto the valve member by the exhaust gaspressure. In order to carry out the opening operation of the valvemember 34a by a smaller working force, in this third embodiment, anopening and shutting lever 38c secured on the support shaft 40a of thevalve member 34a and an opening and shutting lever 38d secured on thesupport shaft 40b of the valve member 34b are connected with each otherby means of a link 38f so that in the opening operation of the valvemember 34a, an actuator 50b for actuating the valve member 34b in anexhaust gas passage with a smaller flow passage area, this is theexhaust gas passage B, assists the opening of the valve member 34a to beeffected by the actuator 50a. One end of the link 38f is pivotallysecured on the lever 38d and actuator 50b. On the other hand, the lever38c is engaged and pivotally supported, for sliding a given distance, inan elongate hole 38g formed on the other end of the link 38f by way of apin 38p secured on its one end, and the other end of the lever 38c ispivotally secured on the actuator 50a.

Next, the operation of the link mechanism which assists the opening ofthe valve member 34a in the exhaust gas passage A with a larger flowpassage area, will be described. FIG. 17 shows the state that the valvemember 34a is closed and the valve member 34b in the exhaust gas passageB with a smaller flow passage area is opened. When the valve member 34ais opened and the valve member 34b is shut from this state, theactuators 50a, 50b rotate the levers 38c, 38d counterclockwise, seen inthe drawing, toward the dotted line positions, respectively. At thattime, the working force of the actuator 50b is applied to the lever 38cby way of the link 38f through the engagement of the pin 38p of thelever 38c with the right end (seen in the drawing) of the elongate hole38g of the link 38f so as to assist the opening of the valve member 34ato be effected by the actuator 50a. When only the valve member 34b isactuated to open from that state, however, the lever 38d is rotatedclockwise (seen in the drawing) by means of the actuator 50b, wherebythe elongate hole 38g of the link 38f is merely caused to slide withrespect to the pin 38p secured on the lever 38c.

From this construction, the opening of the valve member 34a with alarger flow passage area can be assisted by the actuator 50b for thevalve member 34b with a smaller flow passage area, and it is thereforepossible to eliminate the useless oversizing of the actuator 50a and toaim the compacting of the whole device.

In the aforementioned embodiment, both the actuators 50a, 50b arepositioned at both the sides of the exhaust manifold 26, but they can bearranged in parallel on either side. In this case, it is possible tomore compact the whole device.

In addition, the abovementioned link mechanism can be also used in theturbocharger device according to the aforementioned first embodimentwherein the valve members of the valve means are adapted to open towardthe downstream side with respect to the valve seats. In this case, thelink mechanism can assist a working force for shutting the valve member34a in the exhaust gas passage A with a larger flow passage area.

The fourth embodiment according to the present invention shown in FIG.18 and FIG. 19 is one in which the inner circumferential end of thepartition wall 20 of the turbine housing 18 in the first and secondembodiments is not integrated with the same partition wall, but aseparate body therefrom.

The partition wall 20 is more heated in the portion nearer to its innercircumferential side, and the turbine housing 18 on the partition wall20 may be therefore broken owing to the thermal stress caused by thedifference in thermal expansion between the turbine housing on the outercircumferential side and the partition wall on the inner circumferentialside. Since it is difficult to form the partition wall 20 so that itgives access to the outer peripheral edge of the turbine rotor 16because of its manufacturing technique, the clearance between thepartition wall and the turbine rotor becomes large, with resulting inthe quick enlargement of the exhaust gas passage which leads from thefore end of the partition wall to the turbine rotor, and the loss ofenergy is caused.

As shown in FIG. 18, there is fitted an annular end member 21 made asanother body to the inner circumferential part of the partition wall 20through a manufacturing method which will be described below. The end ofthe end member 21 is adapted to approach the outer peripheral edge ofthe turbine rotor 16. As a result, the exhaust gas passages A, B eachare not enlarged quickly in their portion which leads to the outerperipheral edge of the turbine rotor 16, and they are mainly devised tolead to the turbine rotor 16 smoothly.

Since the end member 21 is made of another material which has acoefficient of thermal expansion lower than that of the material of theturbine housing 18, the thermal expansions of the end member 21 and theturbine housing 18 become almost equal to each other, even if the endmember 21 is more heated than the turbine housing 18. Thus, thermalstress between the end member 21 and the turbine housing 18 isprevented. For example, maltensitic stainless steel can be used as amaterial with a lower coefficient of thermal expansion for the endmember 21, and spherical graphite cast iron as a material for theturbine housing 18.

Owing to this composition aforementioned, the turbine housing 18 andpartition wall 20 are heated by high temperature exhaust gas flowingthereinto in the operation of the turbocharger device 10, and inparticular the end member 21 at the inner circumference of the partitionwall 20 is more heated than the turbine housing 18 and the outercircumferential side of the partition wall 20, because it has noradiating portion and is in better contact with the high temperaturegas. But, since the end member 21 is made of a material which has acoefficient of thermal expansion lower than that of the turbine housing18, it does not expand as compared with a case in which they are made ofthe same material. Accordingly, it is possible to prevent the turbinehousing 18 and partition wall 20 from being broken for a long period oftime, because the difference in thermal expansion between the turbinehousing 18 and the partition wall 20 and end member 21 is lowered andthe generation of the thermal stress is reduced.

Next, a method for manufacturing the partition wall 20 and turbinehousing 18 will be described.

A core N which corresponds to the interior contour of a turbine housing18 is first formed as shown in FIG. 19. In the manufacture of the coreN, an end member 21 formed precisely is embedded in the axial center ofthe core N, but the outer circumferential part of the end member 21 isleft exposed a little. At that time, the core N and the end member 21are bonded each other.

Then, a molten metal is poured into a mold with the core N set therein,thereby to cast the turbine housing 18. After cooling the mold, the coreN is removed therefrom. At that time, the end member 21 is formed insuch a state that its outer circumferential part exposed asabovementioned is embedded in the inner circumferential part of thepartition wall 20 protrudedly formed on the turbine housing 18.

Thus, the end member 21 can be mounted so that its end is close to theouter peripheral edge of the turbine rotor 16.

In the way, the clearance δ between the outer peripheral edge of theturbine rotor 16 and the end of the end member 21 can be reduced toabout 2 mm.

In an ordinary casting process, the quick enlargement of an exhaust gaspassage has been inevitable, because it is impossible to form a turbinehousing so that its partition wall has a given clearance below 3 mm.According to the aforementioned method, on the contrary, it is possibleto avoid the quick enlargement of the exhaust gas passage and to preventthe loss of energy caused by that enlargement.

By forming the end member 21 so that it has a smooth shape of curve, theexhaust gas passage which leads from the exhaust gas passages A, B tothe turbine rotor 16 can be formed as a passage which changes gently,thereby to eliminate a quick enlarged portion in the exhaust gaspassage.

Although the end member 21 has been fitted on the turbine housing 18through the casting process stated above, in the abovementionedembodiment, it is possible to carry out the fitting of the end member 21also through another process such as welding or brazing.

FIGS. 20 to 22 show different modifications of the annular member 21 inthe fourth embodiment, in which its deformation owing to the thermalstress is prevented.

The inner circumferential part of the end member 21 undergoes thermalstress caused by exhaust gas, and it will be easily deformed or damagedby the thermal stress. In FIG. 20 and FIG. 21, there are provided as acountermeasure thereto one or more radial slits 21a on the innercircumferential part of the end member 21 or on both the inner and outercircumferential parts thereof, whereby the deformation of the end memberto its circumferential direction caused by the thermal stress can beabsorbed to prevent its breakage. In FIG. 22, furthermore, the endmember 21 is made in a divided structure wherein raidal slits 21b areformed on the end member 21, after it is secured on the partition wall20.

The modification of the aforementioned fourth embodiment, shown in FIG.23, is devised to prevent the exhaust gas passage B from beingcontracted by the deformation of the end member 21 owing to thermalstress, with its end caused to come down to the side of the exhaust gaspassage B. To this end, on the side wall of the turbine housing whichdemarcates the exhaust gas passage B, one or more pins 21c are fixed soas to face to and contact with the portion of the end member 21 whichwill be primarily thermally deformed.

In the fifth embodiment according to the present invention shown inFIGS. 24 to 26, an exhaust braking function which is exhibitedthroughout the whole area of an engine speed is added to thevariable-volume turbocharger device of the first and second embodiment.

Since the turbocharger devices 10 shown in FIG. 1 and FIG. 10 aresubstantially different from each other only in the viewpoint of thearrangement of the valve means, the exhaust braking function will bedescribed below in relation only to the turbocharger device of FIG. 1.But, the description in the matter of the exhaust braking function maybe also applied to the turbocharger device of FIG. 10. In addition, thedescription will be made only about the exhaust braking function,because the structure of the turbocharger device 10 in this embodimentitself is entirely the same as one shown in FIG. 1.

In FIG. 24, a valve control mechanism, diagrammatically indicated at C,is provided on the rocker arms 38a, 38b of the valve means. This valvecontrol mechanism C is composed of actuators 50a, 50b, a hydraulicpressure source 51 for feeding a working pressure to both the actuators,and a controller 52 connected to an exhaust pressure sensor 53 providedin the exhaust manifold 26 so as to carry out the feedback control ofthe valve control mechanism C.

The controller 52 is so composed as to effect the operations in theflowchart shown in FIG. 25.

On the basis of the opening and shutting signals for the valve meanswhich are output from the so-composed controller 52, the actuators 50a,50b are actuated to drive the rocker arms 38a, 38b and the valve members34a, 34b are operated to open or close, whereby the inside of theexhaust manifold 26 at the upstream side of the valve members 34a, 34bis kept at the maximum pressure which is below a predetermined pressurePeo.

When the engine is caused to effect the exhaust braking, an exhaustbraking switch (not shown) is turned on, as shown at the step S1 of FIG.25.

The step S2 is, thereby, carried out in the controller 52 and theactuators 50a, 50b are driven so that the valve members 34a, 34b arecompletely closed.

Next, the step S3 is carried out wherein the exhaust pressure Pe in theexhaust manifold 26 is detected by the exhaust pressure sensor 53 andtransmitted to the controller 52.

In the controller 52, the step S4 is carried out, wherein it is judgedwhether the exhaust pressure Pe is lower than the pressure Peopreviously set in the controller 52. When "YES", the step S5 will bethen carried out.

At the step S5, it is judged whether the valve members 34a, 34b areclosed or not. In the case "YES", that closed state of them ismaintained as it stands.

But, when it is "No", the actuators 50a, 50b are actuated to shut thevalve members 34a, 34b, and the steps S3 to S6 are thereafter repeated.

On the other hand, when it has been judged that the exhaust pressure Pein the exhaust manifold 26 is larger than the pressure Peo at the stepS4, the normal route is not applied and the step S7 is carried out,wherein either of the actuators 50a (or 50b) is actuated, thereby toopen the corresponding valve member 34a (or 34b).

Thus, the step S4, step S7 and step S3 are repeated until the exhaustpressure Pe becomes below the pressure Peo, and the opening of the valvemember 34a is controlled so that the exhaust pressure Pe is below thepressure Peo.

Through these operations, there will be obtained such an exhaust brakingeffect as mentioned below.

In a case that an engine is operated in a low speed area, the exhaustpressure Pe does not reach a pressure over said predetermined pressurewhich has bad influences upon a valve actuating system, and either valvemember 34a (or 34b) is not actuated to open against the air pressure inthe actuator 50a (or 50b). Thus, the exhaust pressure Pe is completelysealed and the braking effect which is caused by the maximum exhaustpressure Pe at that engine speed can be obtained.

Furthermore, in the case that the engine is operated in a medium or highspeed area, the valve member 34a is actuated to open against the airpressure in the actuator 50a, on the basis of the indication signals ofthe controller 52, when the exhaust gas Pe becomes over the pressure Peoin the result of the shutting of the valve members 34a, 34b. Through thefeedback control which leads from the step S3 to the step S7, the valvemember 34a is then opened at a position where the pressing force causedby the actuator 50a and the exhaust pressure Pe are balanced, thereby tokeep the exhaust pressure Pe in the exhaust manifold 26 at the pressurePeo.

In a conventional technique, as shown by the dotted line in FIG. 26, anexhaust pressure Pe which can obtain the exhaust braking effect changeswith an engine speed, and an exhaust braking valve has a small holeperforated therein so as to obtain a predetermined pressure Peo when theengine speed is high. Thus, it has such a characteristic that theexhaust pressure Peo is remarkably lowered when the engine speed is low.

According to the device of this embodiment, however, the valve members34a, 34b are kept closed when the exhaust pressure Pe in the exhaustmanifold 26 is lower than the predetermined pressure Peo, and theopenings of these valve members are automatically controlled by way ofthe controller 52 so that the exhaust pressure Pe is made to be thepredetermined pressure Peo when the exhaust pressure Pe has become overthe pressure Peo. In spite of the engine speed, therefore, the maximumexhaust pressure Pe at that engine speed, with a limitation of thepredetermined pressure Peo, acts as the exhaust pressure Pe for theexhaust braking.

Thus, the device according to this invention can obtain a satisfactoryexhaust braking effect throughout the whole area of engine speed.

Assuming that the air pressure in the actuator 50a (or 50b) is Pa, thepressure-receiving area of the actuator 50a is Aa, the force of thereturn spring 54a (or 54b) of the actuator is Fs and thepressure-receiving area of the valve member 34a (or 34b) is Av, theforce which acts upon the valve member 34a (or 34b) will be representedby the formula (PaAa--Fs). These factors Pa, Aa and Fs are set so as tosatisfy the following expression;

    PaAa-Fs=AvPeo.

Namely, when the exhaust pressure Pe is over the predetermined pressurePeo (Pe>Peo), the following inequality will be satisfied;

    PaAa-Fs=AvPeo<AvPe.

And just then, the valve member 34a (34b) is forced to open and itsopening is automatically controlled so as to satisfy the followingexpressions;

    PaAa-Fs=AvPeo=AvPe.

Thus, the supercharge of air with good efficiency can be carried out andat the same time, the exhaust braking effect can be obtained withaccuracy, by means of the turbocharger device 10.

The use of the abovementioned exhaust braking device makes aconventional exhaust brake useless and the reduction of cost realizable.

The opening and shutting operation of the valve means in thevariable-volume turbocharger devcie which has been described withreference to FIG. 1, FIG. 5 and FIG. 6, is devised to be controlled uponthe engine speed and load. When an accelerator pedal is released, suchas a gear shifting is operated during travelling, according to thiscontrol method, the exhaust gas turbine 12 will be therefore operated,owing to the reduction in engine speed and load caused at that time, inthe region B₃ of FIG. 6, this is under such a state that the flowpassage area of its exhaust gas passage is the maximum (with the flowcharacteristic B₃ shown in FIG. 5) and in other words, the boostpressure of the compressor 14 is lower. As a result, a period of timeuntil the engine speed which matches for a given torque is achieved bydepressing the accelerator pedal again becomes larger. As a result, therising of the exhaust gas turbine until the given torque is achievedafter the gear shifting operation is late and the responsibility of theengine to the depression of the accelerator pedal is bad.

The first control method for improving the transient responsibility ofthe engine at the re-depression of the accelerator pedal will bedescribed with reference to FIGS. 27 to 30.

The structure of a variable-volume turbocharger device 10 shown in FIG.27 is that actuators 50a, 50b and a controller 52 similar to these ofthe aforementioned fifth embodiment are incorporated in the turbochargerdevice of the aforementioned second embodiment. In addition, thestructure of the turbocharger device itself is the same as that of thefirst embodiment.

In this first control method, it is devised that the opening andshutting operation of the valve means is controlled in accordance withthe state of depression (on-off) of the accelerator pedal as well as thestate of the engine speed and load (the accelerator opening). This stateof depression of the accelerator pedal is detected by means of anaccelerator pedal sensor such as a known microswitch. Regardless of theload, in the case that the engine speed is lower than a low rotationspeed Neo previously set and the accelerator pedal has been depressed,or when the accelerator pedal is released in the case that the enginespeed is over Neo and the engine is in a low load operation, asillustrated in the operation characteristic diagram of FIG. 28 and inthe operational mode diagrams of FIGS. 29 and 30, the actuators 50a, 50bare controlled by means of the controller 52, whereby only the valvemember 34b for the exhaust gas passage B with a small flow passage areais opened and the exhaust gas turbine 12 is operated with its flowpassage area set at the minimum (this is, with the flow characteristicB₁ shown in FIG. 5). As can be seen from FIG. 29, in addition, it may becarried out to maintain the flow passage area at the minimum only for agiven period of time t, after the accelerator pedal is depressed againafter its release.

By such a setting, the region B₁ is expanded widely as shown in FIG. 28,in comparison with FIG. 6, and as a result, the transient responsibilityof the engine at the re-depression of the accelerator pedal is improved.

In the operation control method of the aforementioned first embodiment,the exhaust gas turbine 12 is operated under such a state that the flowpassage area of its exhaust gas passage is the maximum (with the flowcharacteristic B₃ in FIG. 5), and in other words, the boost pressure ofthe compressor 14 is low, even when the engine is in a low loadoperation. Therefore, the speed up of the exhaust gas turbine 12 at thetime when the engine load is increased by depressing the accelerator andthe response of the engine is bad.

Next, the second control method for improving the transientresponsiblity of an engine at the increase of its load will be describedhere with reference to FIG. 31.

In this second control method, the exhaust gas turbine 12 is controlledin response to the state of the engine speed and load, but the engineload is detected from the accelerator opening α of the accelerator pedalby use of a known sensor. When the engine is in a low load operation inwhich the accelerator opening α is small than the first set value α₁ andan engine load is small, as shown in FIG. 31, the exhaust gas turbine 12is operated with its flow passage area set at the minimum (this is, withthe flow characteristic B₁ shown FIG. 5), regardless of the enginespeed, by means of the controller 52. In a case that the acceleratoropening α is larger than the first set value α₁ or the second set valueα₂, the flow passage area of the exhaust gas turbine 12, this is itsflow characteristic, is controlled in response to the load state andengine speed, simillarly to the first embodiment.

By such a setting, the region B₁ shown in FIG. 31 can be obtained whenthe accelerator opening is small and the engine load is also small, andas a result, the transient responsibility of the engine at thedepression of the accelerator pedal or at the time when the engine loadis increased, is improved.

When driving a truck, bus or the like, a driver often conducts a gearshift-down operation, with operating a double clutching. In this case,this gear shift-down operation is normally carried out after anaccelerator pedal is depressed at the neutral position among the speedchange gears of a transmission to increase the engine speed. If themethod of the aforementioned first embodiment in which the exhaust gasturbine 12 is controlled only upon the engine speed and load state isapplied at that time, the exhaust gas passage A with a larger flowpassage area will be opened and the speed of the turbine rotor 16 willbe lowered when the accelerator pedal is depressed to increase theengine speed. The responsibility of the engine at the time when theaccelerator pedal is depressed again is therefore bad.

The third control method for improving the transient responsibility ofan engine at the gear shift-down operation will be practiced as follows.As shown in FIG. 27, the opening and shutting operation of the valvemeans is controlled in response to the engine speed and load state andfurther to the speed change gear signals from a known sensor fordetecting whether the speed change gear of a transmission is in aneutral position. When the neutral position is detected from the speedchange gear signal, the actuators 50a, 50b are controlled by thecontroller 52, regardless of the engine speed and load, and only thevalve member 34b in the exhaust gas passage B with a smaller flowpassage area is opened, whereby the exhaust gas turbine 12 is operatedwith its flow passage area set at the minimum (this is, with the flowcharacteristic B₁ shown in FIG. 5). In the result, the turbine rotor 16is maintained as it is rotated at a high speed and the transientresponsibility of the engine at the next depression of the acceleratorpedal is improved.

What is claimed:
 1. A variable-volume turbocharger device comprising aturbine housing having at least first and second exhaust gas passagesdivided by a partition wall provided in the housing, said first exhaustgas passage having a large flow characteristic and said second exhaustgas pasage having a small flow characteristic, a first valve meansoperable to open and shut said first exhaust gas passage, and a secondvalve means operative to open and shut said second exhaust gas passageindependently from said first valve means, each of said valve meanshaving a valve member which cooperates with a valve seat to open andshut the corresponding exhaust gas passage, said valve members beingarranged so as to open toward the upstream side of the flowing directionof exhaust gas with respect to said valve seats.
 2. A variable-volumeturbocharger device, as set forth in claim 1, which further comprises avalve control mechanism responsive to the operating conditions of anengine associated with said turbocharger to open either one or both ofsaid first and second valve means so as to provide three differentturbine characteristics of large, medium and small flow rates.
 3. Avariable-volume turbocharger device, as set forth in claim 1, in whichsaid turbine housing has inlets each leading to said exhaust gaspassages, a valve casing with said valve seats provided thereon isinterposed between said inlets and an exhaust device of an engine, andsaid valve members each are movably supported on rocker arms pivotallysupported on said valve casing, with a clearance existing between them.4. A variable-volume turbocharger device, as set forth in claim 1, inwhich said turbine housing has inlets each leading to said exhaust gaspassages, said valve seats are provided on said inlets, and said valvemembers each are movably supported on rocker arms pivotally supported onsaid turbine housing, with a clearance existing between them.
 5. Avariable-volume turbocharger device, as set forth in claim 1, in whichsaid valve members each are movably supported on rocker arms arrangedfor pivotal movement, with a clearance existing between them, and asupporting point of each of said valve members to the rocker arm isoffset toward the center of the pivotal movement of said rocker arm,with respect to the working center point of an exhaust gas pressureacting upon the valve member.
 6. A variable-volume turbocharger device,as set forth in claim 1, in which it further comprises a valve controlmechanism which keeps the closed state of said valve means when anexhaust pressure at the upstream side of the valve means is below apredetermined pressure and causes either one of said valve means to openwhen the exhaust pressure is increased over the predetermined pressure,during the braking operation, an exhaust pressure sensor for detectingthe exhaust pressure at the upstream side of said valve means, and acontroller for outputting the opening and shutting signals for saidvalve means to said valve control mechanism on the basis of thedetection signals of said exhaust pressure sensor.
 7. A variable-volumeturbocharger device, as set forth in claim 1, in whcih said valve meansare actuated to open or shut by actuators, respectively, and saidactuators are linked to each other so as to assist a working force forshutting one of said valve means.
 8. A variable-volume turbochargerdevice, as set forth in claim 1, in which said valve means are actuatedto open or shut by actuators, respectively, and said actuators arelinked to each other so as to assist a working force for opening one ofsaid valve means.
 9. A variable-volume turbocharger device, as set forthin claim 1, in which said turbine housing has inlets each leading tosaid exhaust gas passages, the valve seats are provided on said inlets,and said valve members each are movably supported on rocker armspivotally supported on an exhaust manifold of an engine, with aclearance existing between the.
 10. A variable-volume turbochargerdevice, as set forth in claim 9, in which each of said valve members ismade in the shape of a rectangle and prevented from its turning to thecorresponding rocker arm by means of a turn preventing means.
 11. Avariable-volume turbocharger device, as set forth in claim 9, in whicheach of said rocker arms is secured on a support shaft pivotallysupported by way of a fixed bush, and said bush is made of martensiticchromium carbide-precipitated steel and said support shaft is made ofmartensitic steel.
 12. A variable-volume turbocharger device, as setforth in claim 9, in which each of said rocker arms is secured on asupport shaft pivotally supported by way of a fixed bush, and said bushis made of ceramic and said support shaft is made of martensiticchromium carbide-precipitated steel.